Organic light-emitting diodes OLEDs are known in the art. For example, Kido et al. (U.S. Pat. No. 6,013,384) discloses, as shown in FIG. 1a, an organic electroluminescent device 10 wherein the organic layers consist of a hole transport layer (HTL) 13, an emissive layer 14 and a metal-doped organic compound layer 15 disposed between an anode layer 12 and a cathode layer 16. The device is fabricated on a substrate 11. According to Kido et al., the organic compounds which can be used in the formation of the emissive layer, the electron transport layer and the metal-doped layer in the OLED device, include polycyclic compounds, condensed polycyclic hydrocarbon compounds, condensed heterocyclic compounds, etc. The dopant in the metal-doped organic compound layer is a metal having a work function of less than or equal to 4.2 eV. The emissive layer can be made of 8-tris-hydroxyquinoline aluminum (Alq3) among many metal-chelated complex compounds, for example. The hole transport layer 13, as well as a hole injection layer, can be made of an arylamine compound. The anode layer 12 is made of ITO and the cathode 16 is an aluminum layer.
Weaver et al. (U.S. Publication No. 2004/0032206 A1) discloses another OLED including an alkali metal compound layer. As shown in FIG. 1b, the OLED 20 is fabricated on a plastic substrate 21 pre-coated with an ITO anode 22. The cathode consists of two layers: a metal oxide layer 28 deposited over a layer 27 of Mg or Mg alloy. The alkali metal compound layer 26 can be made of alkali halides or alkali oxides such as LiF and Li2O. The organic layers include an HTL layer 23, an emissive layer (EML) 24 and an electron transport layer (ETL) 25. In particular, a layer of copper-phthalocyanine (CuPc) is deposited to a thickness of about 10 nm thick over the ITO anode 22 to improve hole injection and device lifetime. The HTL 23 of 4,4′-[N-(1-naphthyl)-N-phenyl-amino]biphenyl (NPB) is deposited to a thickness of about 30 nm over the CuPc. The EML 24 of 4,4′-N,N′-dicarbazole-biphenyl (CBP) doped with fac-tris(2-phenylpyridine-)-iridium (Ir(ppy)3) is deposited to a thickness of 30 nm over the NPB. A hole blocking layer of aluminum(III)bis(2-methyl-8-quinolinato)4-phenylphenolate (BAlq) is deposited to a thickness of about 10 nm over the EML. The ETL 25 of Alq3 is deposited to a thickness of about 40 μm over the BAlq. The layer 26 of LiF about 0.5-1 nm thick is deposited after the Alq3 and before the Mg alloy (including Mg:Ag).
Raychaudhuri et al. (U.S. Pat. No. 6,579,629 B1) discloses an OLED 30 (see FIG. 1c) wherein the anode 32 is made from ITO disposed on a substrate 31; the HIL 33 is made from a fluorinated polymer CFx, where x is 1 or 2; the HTL 34 is made from an aromatic tertiary amine such as NPB; the EML 35 is made from Alq3:C545T, with C545T being 1H,5H,11H-[1]Benzopyrano[6,7,8-ij]quinolizin-11-one, 10-(2-benzothiazolyl)-2,3,6,7-tetrahydro-1,1,7,7-tetramethyl-(9CI); the ETL 36 is made from Alq3, the buffer structure comprises a first buffer layer 37 made from LiF, and a second buffer layer 38 made from CuPc; and the cathode is made from Al:Li (3 w %).
Hung et al. (U.S. Pat. No. 5,776,623) discloses an electroluminescent device 40 (see FIG. 1d) wherein the HIL 43 is a 15 nm-thick CuPc layer deposited over the anode layer 42 on top of a substrate 41; the HTL 44 is a 60 nm-thick NPB layer; the ETL 45 is a 75 nm-thick Alq3 layer. The buffer layer 46 is a 0.5 nm-thick lithium fluoride (LiF) layer. The lithium fluoride layer can be replaced by magnesium fluoride (MgF2), calcium fluoride (CaF2), lithium oxide (Li2O) or magnesium oxide (MgO). The cathode layer 48 can be made from aluminum and Mg:Ag. Ag and Au are also used in the cathode layer.
In the above-mentioned OLEDs, at least the EML and HTL are made from different materials. In Weaver et al., the ETL and the EML are also made from different materials. When the HIL, HTL, EML and ETL are made from different organic materials, it is required to have four different deposition channels to separately deposit the different organic materials in order to avoid cross contamination in the fabrication process. In the fabrication of a full-color organic display device, the deposition of the organic layers is complex and costly.
It is thus advantageous and desirable to provide a method for producing an organic light-emitting device wherein the number of different organic deposition channels can be reduced.